This invention relates to a method of making an abrasive compact.
Abrasive compacts are used extensively in cutting, milling, grinding, drilling and other abrasive operations. Abrasive compacts consist of a mass of diamond or cubic boron nitride particles bonded into a coherent, polycrystalline conglomerate. The abrasive particle content of abrasive compacts is high and there is generally an extensive amount of direct particle-to-particle bonding. Abrasive compacts are generally made under elevated temperature and pressure conditions at which the abrasive particle, be it diamond or cubic boron nitride, is crystallographically stable.
Abrasive compacts tend to be brittle and in use they are frequently supported by being bonded to a cemented carbide substrate or support. Such supported abrasive compacts are known in the art as composite abrasive compacts. Composite abrasive compacts may be used as such in a working surface of an abrasive tool.
Examples of composite abrasive compacts can be found described in U.S. Pat. Nos. 3,745,623, 3,767,371 and 3,743,489.
Composite abrasive compacts are generally produced by placing the components, in particulate form, necessary to form an abrasive compact on a cemented carbide substrate. This unbonded assembly is placed in a reaction capsule which is then placed in the reaction zone of a conventional high pressure/high temperature apparatus. The contents of the reaction capsule are subjected to suitable conditions of elevated temperature and pressure.
U.S. Pat. No. 4,861,350 describes a tool component comprising an abrasive compact bonded to a cemented carbide support in which the abrasive compact has two zones which are joined by an interlocking, common boundary. The one zone provides the cutting edge or point for the tool component, while the other zone is bonded to the cemented carbide support. In one embodiment of the tool component, the zone which provides the cutting edge or point has ultra-hard abrasive particles which are finer than the ultra-hard abrasive particles in the other zone. There is no disclosure of using a mixture of ultra-hard abrasive particles of different particle size.
U.S. Pat. No. 4,311,490 describes an abrasive compact wherein the bonded abrasive particles comprise a coarse layer and a fine layer. Again, the use of a mixture of abrasive particles of different particle size is not disclosed.
U.S. Pat. No. 4,604,106 describes a composite diamond abrasive compact comprising at least one layer of diamond crystals and pre-cemented carbide pieces which have been pressed under severe heat and pressure to create a composite polycrystalline material wherein polycrystalline diamond and pre-cemented carbide pieces are interspersed in one another. In one embodiment, a mixture of diamond particles is used, 65 percent of the particles being of the size 4 to 8 microns and 35 percent being of the size 0.5 to 1 micron.
U.S. Patent No. 5,011,514 describes a thermally stable diamond compact comprising a plurality of individually metal-coated diamond particles wherein the metal coatings between adjacent particles are bonded to each other forming a cemented matrix. Examples of the metal coating are carbide formers such as tungsten, tantalum and molybdenum. The individually metal-coated diamond particles are bonded under diamond synthesis temperature and pressure conditions. The patent further discloses mixing the metal-coated diamond particles with uncoated smaller sized diamond particles which lie in the interstices between the coated particles. The smaller particles are said to decrease the porosity and increase the diamond content of the compact. Examples of bimodal compacts, i.e. two different particle sizes, and trimodal compacts, three different particles sizes, are described.